Understanding the activity-stability trade-off for low-cost vanadium-doped Co₂C-Mo₂C for efficient hydrogen evolution reaction in PEM water electrolysis

Hydrogen production through proton exchange membrane water electrolysis (PEMWE) continues to rely predominantly on platinum-group metals, which restricts both cost efficiency and long-term durability. Here, we present vanadium single-atom (V_SA) doped Co₂C-Mo₂C nanosheets (V_SA@Co₂C-Mo₂C) that integrate single-atom doping chemistry with a coherent carbide–carbide heterointerface, effectively addressing the activity-stability trade-off. A scalable, dopamine-assisted hydrothermal and carbonization method produces ultrathin, porous nanosheets that are uniformly anchored onto carbon cloth, featuring intergrown Co₂C and Mo₂C nanodomains as well as atomically dispersed vanadium. This catalyst achieves hydrogen-evolution overpotentials of 61, 89, and 121 mV at 10 mA cm⁻² in 0.5 M H₂SO₄, 1.0 M KOH, and 1.0 M PBS, respectively, combined with favorable Tafel slopes, low charge-transfer resistance, enhanced electrochemically active surface area, and operational stability for 100 h across a range of pH values. In situ Raman spectroscopy identifies pronounced Co-H and Mo-H bands, whose intensities are accentuated in acidic and alkaline environments, correlating with low overpotentials; contact-angle assessment further confirms superior surface wettability. Density functional theory (DFT) calculations demonstrate that V incorporation and the Co₂C-Mo₂C heterojunction collectively enhance the density of states at the Fermi level and optimally adjust ΔG_H* toward a near-zero value (-0.086 eV), where Mo sites are marginally dominant. When applied as a PEMWE cathode at 70 °C, V_SA@Co₂C-Mo₂C reaches 0.5 A cm⁻² at 1.80 V and maintains stable operation over 500 h, establishing a noble-metal-free, pH-universal HER catalyst suitable for integration with PEMWE.